Abrasive wheel



lApril 13, 1937. E. VANDER PYL ABRASIVE WHEEL Filed Aug. 2, 1935 fill Il lfl/ /l l EDWARD VAN DER Pw.

atented Apr. 13, 1937 masiva warm.

Edward Van. der liyl, Heiden, Mass., assigner to Norton Company, Worcester, Mass., a corporation oi Massachusetts Application August 2, 1935, Serial No. 34,407

3 i'llaims..

The invention relates to abrasive wheels and a method of making the same.,

One objectof the invention is to provide a grinding wheel for grinding very hard substances.

5 Another object of the invention is to provide abond and a method of bonding particularly suitable for the manufacture of grinding or lapping wheels the abrasive part of which includes diamonds. Another object of the invention is to l provide a bond for diamond abrasive from which the diamonds may be recovered at small expense and without destruction of the diamonds. Another object of the invention is to vprovide a bond which itself will break down but which neverl theless will hold the abrasive grain so long as free cutting edges are presented. Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the feam tures of construction, combinations of elements, arrangements of parts, and in the several steps and relation and order of each of said steps to one or more of the others thereof, all as will be illustratively described herein, and the scope of the application of 'which will be indicated in the following claims.

In `the accompanying drawing in which is shown one of various possible embodiments of the mechanical features of this invention, the single view is a vertical axial cross section through an electric furnace and pressure apparatus together with a mold which may be 'used to carry out the method of the invention.

I provide aluminum in powdered form which size although other grit may be used. I provide also powdered silicon which may be of the same grit size. Takingin the neighborhood of 60%, by weight, of silicon, and .by weight, aluminum, I mix the powders together thoroughly. This may be done in any convenient manner as by hand or in a ball mill. It should be understood that many dilerent sizes of grain can be used but for the best results I prefer to use fairly ne grain. Instead of mixing grain or powders of aluminum and silicon I may form an alloy of the two metals in the usual manner and then powder them to the size of grain indicated.

This powder or mixture of powders I then mix mond grit which, because of its extreme hardness and its other qualities, constitutes probably the best abrasive substance known, exists in a form commercially known `as bortv which is commercially available in suilicient quantities may be in the neighborhood of 100 mesh grit with the required amount of diamond grit. Diaand at such prices that it may be used for the manufacture of grinding wheels and other abrasive bodies. While bort is expensive, nevertheless on account of the great superiority of the diamond for abradant purposes, the wheel formed thereof has many practical uses vand advantages. With the powdered bond of the type indicated I mix in the neighborhood of between 25 and 50% by volume of such bort, in a grit size oi between mesh and 500 mesh, for example. The mesh size of bort selected will depend upon the abrading operation that the Wheel is to perform, and my invention has no limitations in this respect, in so much as grinding, polishing and lapping operations diler vastly among themselves. For the ilner polishing or lapping operations a iiner grit size of bort will be used.

The mixing of the grain with the bond may be accomplished manually, for although machine methods might be used, the bort or diamond dust is so valuable as to dictate care in the mixing to avoid loss of diamond. Referring now to the drawing, I take a measured quantity of bond and bort and. place it in an annular mold i. This moldi may comprise a cylindrical annulus 2 of graphite. used with success, I prefer to use graphite loecause at the temperature which I prefer to employ in sintering the material, the graphite acts as a protector for the diamond and also the alloy involved by combining with oxygen before it has a chance to reach the materials being molded and sintered. The mold further comprises, in the preferred embodiment of the invention, a pair of annular cylindrical plungers 3 and li, also preferably of graphite :for the reason above given, and whose outside diameter is the inside diameter of the annulus t, and each having a bore 5 and 6 respectively, Acoaxial and of the same diameter and in which is a graphite core 'i fitting with a sliding t.

The annuluses 3 and 4 are in the nature of plungers andjt the annulus 2 with a sliding fit. I place the diamond and bond mixture l0 between the plungers 3 and 4, the core 1.and the annulus 2 as shown, thus filling a cylindrical annular space. Iv then introduce the mold 'I into a furnace capable of producing a temperature of 1400" C. and between pressure apparatus arranged to exert pressure against the plungers 3 and 4 in a true axial direction. Such furnace apparatus and pressure apparatus may take any desired form and my invention is in no wise limited to any particular one, but by way of example I have shown a rigid support or platen While other substances may be l as shown, I bring the plunger I2,down to the II having a horizontal plane surface above which is located a plunger i2 having a lower horizontal plane surface and which plunger I 2 may be moved vertically downward with the required force. Upon the platen II is an annular electric furnace I3 being a molybdenum wound furnace of a type which is well known. Such -a furnace may have a cylindrical refractory core I4 of aluminum oxide having a corrugated outer wall I5 whose convolutions extend helically and have in them helically wound molybdenum wire I6. The aluminum oxide core or shell may rest upon an annular steel disk I'I, and at the top of the furnace there may be an annular steel disk I8..

the disks "I1 and I8 Vbeing connected by a hollow steel cylinder- I9. 'Ihus a space is left surrounding the molybdenum resistance wire IB which space is filled with powdered insulating' material,

such as magnesium oxide.

Having introduced the material I0 into the mold I, and placed the mold I upon the platen I I plunger 3 and energize the furnace I3. The furnace I3 is designed to heat the material being molded to a temperature o f 1400 C. and to avoid oxidation of the molybdenum winding I6 there is provided a nipple 20 which may be connected to a hose for the introduction of an inert gas such as nitrogen or a reducing gas such as hydrogen which permeates the space in which is the magnesium oxide insulation and also escapes through the porous aluminum oxide refractory onto the mold I, thus protecting the mold I from oxidation and further protecting the material I0. Ator before the -attainment of 1400 vC. I cause the plunger I2 to exert a pressure on the material I0 in the neighborhood of 600 lbs. per sq. in. I may,

however, employl more or less pressure and the amount of pressure used will depend upon the porosity which I desire to achieve in the bond and wheel. With more'- pressure I get a denser wheel and withless pressure I get a more porous wheel. For certain types of grinding, I may wish a porous wheel. The material may be sintered at the temperature specified by'pressure as low as 50 lbs. per sq. in. On the other hand, I may use a lower temperature to produce a more porous bond or with higher pressure to produce the same porosity. "I'hus the pressure employed may vary between wide limits and in certain cases I may use a pressure as high as 3000 lbs. per sq. in. Merely by way of example I note that for the production of a fairlydense and strong wheel using diamond grit sizeof mesh and bond grit size of 200 mesh and a temperature of 1400 C., a pressure of 600 lbs. per sq. in. was employed.

Although I prefer to apply pressure and heat simultaneously, in certain cases I may attain excellent results applying them seriatim, the mixture being pressed rst and Aheated afterwards. 'Ihis is because the intimate contact for fusion sintering persists after the mixture is compacted.

The heating, however, substantially changes the characteristics of the ultimate product.

I may remove the mold I as soon as the pressure is relieved and quench it in water. This will tend to make the bond more brittle. In such event the mold I is generally destroyed, but the loss is not great and the value of theresulting product'is such that this need not be considered a vital factor. However, I may use the mold parts over and over again in case they are allowed to cool without quenching. For certain types of wheels I may prefer a somewhat softer bond.

Due to the extreme hardness and resistance to wear of the diamond when used as an abrasive compared with the commonly used types such as silicon carbide and aluminum oxide, it is desired to provide a bond of a suillcient strength and hardness to hold the individual particle until it becomes too dull for efcient cutting or abrading action. When that point is reached, however, and by means of the additional force. applied to the particle when dull, it is desired that the particle should be either pulled out or reforiented to present respectively a new particle or a new cutting point.

1, therefore, desire a bond which although brittle will under the grinding action maintain or develop a limited degree of ductility. A wheel to be tough and strong considered as a whole, and

is free cutting and has' excellent abrading characteristics. I believe the excellent results achieved by so constructing a wheel to be due tothe intrinsic properties of the alloy used and also tothe fact that it does not completely alloy. 'I'he alloy itself has a brittle characteristic while one of its ingredients, aluminum, has a ductile characteristic. Thus, although it is apparently impossible to have in a single substance both ductlity and brittleness, unless considered relatively, I have achieved ductility and brittleness in my bond which may be due to the fact that it is not entirely homogeneous; nevertheless it is homogeneous enough to form an integral mass.

Although certain advantages inhere from the use of aluminum and silicon, it will be understood that the method -of the invention involving the use of heat and pressure and the sintering of a. bond in grain form maybe used in connection with any other metal or metals having a fusion point at or below- 1400 C. or thereabouts. While I have noted 40%- aluminum and 60% silicon by weights, other proportions of these metals may be used, but I prefer to use a fairly large proportion of silicon. However, in the preferred embodiment of my invention itmay be between 50%l and 70%.

One marked advantage of a wheel constructed according to the invention lies in the fact that, when produced in annular form, it may be readily united to a central disk. Diamond grinding wheels are, under present market conditions, expensive, whatever the bond used, owing simply to the high price of bort, and accordingly it is highly desirable to waste as little of the diamond as is possible. In the case of any grinding wheel whichis thin relative to its diameter, thejcentral part will generally not be' used. Accordingly, in the case of diamond wheels, it is preferred to form the central part in the form of a non-grinding disk or annulus. While a small internal grinding wheel, having a length on the order of half its diameter, may comprise 100% grinding substance and be attached by mounting directly upon a spindle, in the case of a cutting-oil' wheel, or a large sized wheel for the grinding of the cemented tungsten carbides and other hard substances, itis generally found economical to secure what amounts to an annular band of diamond grinding material to a central disk, having a hole therein. Therefore, a distinct problem has arisen in attaching the in- If the union between the parts is weak, fracture will result2and this'destroys a. grinding wheel which may have a market value in the neighbor`= hood of from`$50 to $200.

bide as well as diamond should be exposed for as shorta time as possible to high temperatures on account of danger of oxidation and other chemical changes. Furthermore, in actual practice, the preferred bond of this invention has been found excellent in combination with boron carbide grit of a grain size of 100 mesh.` The bond oi." the inventionis more in the nature of a matrix than the common vitried bond, and it is harder and tougher than the artificial resinous bonds, and has properties different from those of a rubber bond, and the properties of the bond of this invention are highly desirable in combination with grain of extreme hardness such as diamond and boron carbide on Mohs scale greater than 9 and harder than silicon carbide.

It will thus be seen that there has been provided by this invention a method and an article of manufacture or composition of matter in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As various possible embodiments might be made of the mechanical features of the above invention and as the art herein described might be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawing is to be interpreted as' illustrative and not in a. limiting sense.

I claim:-

1. An abrasive body comprising diamond grain united with a bond comprising aluminum in the neighborhood of 40 parts and silicon in the neighborhood of parts, the aluminum and the silicon being sintered together and not completely alloyed.

v2. An'abrasive body comprising diamond grain in a bond comprising silicon and aluminum.

3. An abrasive body comprising diamond grain in a bond comprising sintered aluminum and silicon, the silicon and aluminum being sinvtered together and not completely alloyed.

EDWARD VAN DER PYL. 

